Stoker apparatus



June 4, 1957 A. c. STARK 2,794,406

sToKER APPARATUS Filed Sept. 24, 1.952

2 snets-sheet 1 t THERMOCOUPLE PYROMETER CON R03 LER ROTOR SPEED CONTROLVALV CONTROL APPARATUS FIG.I.

RESERVOIR WITNESSES: i INVENTOR ALBERT C. STARK RQQYNTYRM ATTORN EY June 4, 1957 A. c. STARK STKER APPARATUS 2 Sheets-Sheet 2 Filed Sept. 24. 1952 INVENTOR ALBERT c. STARKV ATTORNEY 2,794,406 Patented June 4, 1957 sroma APPARATUS I Albert C. Stark, Morton, Pa., assigner, by mesne assign- This invention relates to stokers and control apparatus therefor, and more particularly to temperature-responsive means for controlling the fuel distributing operation of a Stoker.

With a spreader stoker comprising a fuel feeding device, la fuel impelling device, such as a fuel throwing rotor, and a fuel receiving grate, to realize maximum combustion efliciency it is desirable that the throw of fuel be neither insuiicient nor excessive at or near the wall of the furnace remote from the rotor. Fuel distribution over the grate of such a stocker has heretofore been controlled by manual adjustment of the rotor speed. Under service conditions, however, manual adjustment is uncertain and may be effected too late or cause excessive correction, so that the best combustion efficiency with minimum stack smoke may be obtained only for short periods. As coal size and consist may further vary the distribution as thus effected, undesirable conditions tend to develop, such as loss of attainable combustion eiciency, excessive stack smoke and early deterioration of the refractory wall structure of the furnace.

rIhe temperature at or near the wall remote from the fuel impelling rotor, which may be the rear wall, incident to excessive speed f the rotor of such a Stoker, varies considerably from that attained during rotor operation at insucient speed. lt is an object of the present invention to provide means responsive to this temperature variation to control the rotor speed, thereby automatically maintaining the combustion efciency desired.

Another object of the invention is the provision of stoker control apparatus including a thermocouple pyrometer for indicating relative temperature variations of the fuel bed at or near a Wall of a furnace remote from fuel impelling means supplying the fuel bed, a thermocouple pyrometer controller responsive thereto and reversible motor and linkage means controlled by the pyrometer controllerfor governingthe fuel throw effected by the fuel impelling means.

A further object of the invention is the provision of apparatus of the foregoing description for effecting a reduction in speed of a fuel throwing rotor incident to an increase in temperature in a selected combustion zone, and an increase in rotor speed upon a reduction in such temperature. Y

It is another object to provide Stoker apparatus adapted to-include interrupting timer means for inching the changes in rotor mecd, and transfer switch means operable at will to permit manual control of Stoker operation under certain conditions, such las during ignition or starting of the furnace.

In order to obviate any adverse effect incident to a change in boiler load on the proper operation of apparatus constructed in accordance with the invention, it has been found desirable to provide means for compensating for transitory variations in furnace temperature, as dis- Cinguished from fuel bed temperature. ln controlling a furnace in accordance with boiler load, the pressure in the usual primary air duct, through which cool air is delivered to the furnace, is normally maintained at the required value by operation of a suitable damper adjacent the conventional forced-draft fan at the inlet of the primary air duct. r1`his cooling air flow is thus substantially proportional to boiler load. Employing this fact to advantage, it is a further object of the invention to ensure compensation for the above-mentioned boiler load changes by the provision of means for cooling each furnace ternperature-responsive thermocouple with air supplied from the primary air .duct by way of a restricted passage, the rate of flow of such cooling air being determined partly by the differential between the pressure of air in the duct and the pressure of the furnace atmosphere, and partly by the :dow area of the passage.

An additional object of the invention is to provide improved automatic stoker control apparatus having the aforesaid features of temperature-responsive fuel distribution, in which the thermocouple responsive to fuel bed temperature is cooled at high boiler load but not at zero load, so that the resultant compensated response of the thermocouple will remain, at all boiler loads, a useful indication of the fuel bed temperatures substantially uninuenced by changes in furnace temperature owing to boiler load variations.

These and other objects are effected by the invention `as will be apparent from the following description taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. l is a schematic sectional plan view of a Stoker equipped furnace having associated therewith a preferred form of temperature-responsive rotor control apparatus contructed and arranged in accordance with the invention;

Fig. 2 is a sectional elevational view of a portion of the apparatus shown in Fig. 1; and

Fig. 3 is a fragmentary enlarged `detail sectional View of one of the cooling air compensated thermocouples of the apparatus shown in Fig. l.

Referring to Fig. 2, a typical power plant installation, as shown in elementary form, may comprise opposed Walls such as front and rear furnace walls 10 and 11 serving with suitable side walls toV enclose a boiler structure 12 and a combustion chamber 13. Stoker apparatus is provided comprising a traveling chain grate 14 for supporting a fuel bed, indicated by the reference character 15 over which coal or similar fuel is distributed from a hopper 16 by operation of one or more rotors 17 that are rotatably mounted in a housing 18 carried by the front wall 10. Any other type of fuel distributing or impelling means may be substituted for the rotors 17, if preferred. In the form shown, it will be understood that fuel will be distributed at a rate dependent upon the speed of the rotors 17. Wind box compartments 19 and 20 are suspended from a frame 21 beneath the chain grate 14, and are adapted to be supplied with lair under pressure from a suitable fan (not shown) by way of ducts, such as an air duct 22.

As shown diagrammatically in Fig. l, the rotors 17 are adapted to be driven at selected variable speed by a hydraulic motivating system including a motor 24, which is operative by fluid supplied through a pipe system 2S from a reservoir Z6 by a pump 27, under the control of suitable hydraulic control apparatusy 28, as disclosed in greater detail, for example, in Patent No. 2,603,421, issued to D. I. Mosshart on July 15, 1952, and assigned to the assignee of the present invention.

This hydraulic motivating system is further controlled, according to the present invention, by means of an electroresponsive speed control valve device 30 operable by a reversible motor 31, which is energized in accordance with the suitably amplified energy output of a thermocouple pyrometer control device 32. The structural details of the thermocouple pyrometer controller 32 are not disclosed, since such details are unnecessary for a full understanding of this invention, but it will be understood that this device may be of any well-knownl construction suitable for actuating the rotor speed control valve Vfuel bed 15,

device Y30 in response to the temperature indications of one or more thermocouples 34, which are disposed adjacent the furnace wall remote from the fuel impelling device orV rotors, in this case therear wall 11 of the furnace structure, formeasuring the local temperature Yof the A ,suitable control circuit,35 is provided for connecting the thermocouples in series to the thermocouple pyrometer controller 32.

As best shown in Fig. 3, each thermocoupleY 34 is mounted in a shield or tube y37-having an end opening 38, the tube Vextending through the side wall 11a at an `angle a with the end-opening'direeted toward the fuel bed 15 at or near the rear furnace-wall 11. Each of the tubes 37 has a passageV 38a whichY communicates by 'Way of a restricted'passage -or oriiice39'and a conduit 40 with an air receiving-probe member 42, which extends into-the air duct 22 with the open Aend42a of the probe lmember directed upstream.' Suicient space is left around each thermocouple 34 to allowV flowl of cooling air through the passage 38a and opening 38. Each'thermocouple 34 may readily be adjusted relative to the protecting tube 37 containing it to provide any desired scanning range or angle of survey A of the fuel bed 15, corresponding to the angle of inclination of the tube.

Suitableinterrupting timer means for inching the changes in rotor speed, and transferor changeover means operable to permit manual control lof the rotor speed when desired, may be included in the -control apparatus 28. Such means are well known, and detailed disclosure thereof is consequently not deemedl necessary.

From the foregoing it will thus be seen that, with an improved Stoker control system embodying the invention, the relative temperature of the fuel bed at or near the rear wall of the furnace, as indicatedby the thermocouples 34 is measured for'elfecting 'operation of the thermocouple pyrometer controller32 for actuating a reversible motor with suitable linkage and Vvalve means to govern the speed of the fuel throwing rotors 17, so that-the latter will be driven at a slow rate in response to a temperature -higher than a selected control temperature, orl at a relatively fast rate in responseto a lower temperature. The

Yimproved control system further ensures compensation .for changes in boiler load, in order to prevent such changes from adversely affecting the distribution of fuel called for by the temperature of the fuel bed, by cooling the thermocouples 34 with air taken from the primary air duct 22, the quantity of cooling air being determined by the difference between pressureof airv in the duct and fthat of the furnace` atmosphere, with relation to the ow areas of the restricted passages or orices 39 in the air supply pipe 40. Since the pressure of air maintained in the primary air duct 22 is normally that required for the boiler load, as controlled by a damper (not shown) in cooperation with the usual forced-draft fan (not shown) supplying air to the duct,.this cooling aix` flow is proportional to the boiler load. With this compensation, each thermocouple is cooled at high boiler load, with no cooling at zero load, so that the resultant response of the thermocouple is a substantially accurate indication of the fuel bed temperature with minimum error incident to any change in furnace temperature owing to. load Variation. The Stroker control apparatus, in operation in response to the fuel bed temperature indications of the thermocouples, thus will maintain the desired fuel distribution at all boiler loads.

While the invention has been-shown in but one form, it will be obvious to those skilled inthe art that it is not so limited, but is susceptiblepof various changes and modiiications without departing from the spirit thereof.

What is claimed is:

1. In stroker control apparatus for VaV boiler furnace equipped with a primary air-duct through which air is vsupplied at a high rate when boilerload is high and at a lower rate when boiler-load is low, said-furnace having -a grate for supporting the fuelbed, a motor-driven fuel cooling air to said thermocouple.

throwing rotor, control means for controlling the speed -of said rotor, electro-responsive thermocouple pyrometer energization of said circuit, and conduit means communicating with said air duct and with saidthermocouple means for supplying cooling air from said air duct to said thermocouple means to compensate said thermocouple means for changes in temperature of the furnace atmosphere incident to changes in boiler load.

2. In stoker control apparatus for a boiler furnace equipped with a primaryv air duct through which airis supplied at a high rate when boiler load is high and at a lower rate when boiler load is low, said furnace having opposite first Vand second walls and a grate supporting the fuel bed, a fuel throwing rotor operative near said iirst wall to distribute fuel over said grate, motor means driv- Yingly connected to said rotor, speed control means for varying the speed of said motor in accordance with fuel requirements of the furnace, electro-responsive thermocouple pyrome'ter control means Operative to adjust said speed control means, a control circuit for energizing said thermocouple pyrometer control means, thermocouple means disposednear said second wall of the furnace in heat-responsive relation to a local area of the fuel bed for effecting energization of said circuit in accordance with fuel bed temperature, and conduit means communicating with said air duct and with said thermocouple means for supplying cooling air from said air duct to said thermocouple means to compensate said thennocouple means for changes in temperature of the furnace atmosphere incidentto changes in boiler load.

`3. In Stoker control apparatus for a boiler furnace equipped with a primary air duct through which air is Vsupplied at a high rate when boiler load is high and at a lower rate when boiler load is low, said furnace having opposed first `and second walls and a grate for supporting the fuel bed, in combination, a fuel throwing rotor mounted in the iirst wall of the furnace and operative to distribute fuel over said grate, motor means for driving said rotor at selected speeds in accordance with fuel requirements of the furnace, speed control means operable for controlling the operation of lsaid motor means, electroresponsive thermocouple pyrometer control means for operating said speed control means, a control circuit for energizing said relay means, a hollow shield mounted in said furnacenear the second wall remote from said rotor and having an open end directed toward the fuel bed v supported by said grate, a thermocouple mounted in said shield with clearance forming a How passage, said thermocouple being disposed in heat-responsive relation to the fuel bed and connected to said control circuit, and a conduit communicatingrwith said air duct and with the ow passage in said shield for supplying cooling air to cornpensate said thermocouple Yfor changes in temperature of the furnace atmosphere incident to changes in boiler load.

4. Apparatusl as set forth in claim 3 wherein an orice is interposed in said conduit for controlling the ow of References Cited in the le of this patent UNITED STATES PATENTS 1,393,826 Potter Oct. 18, 1921 1,758,146 Cross May 13, 1930 1,835,089 Roucka Dec. 8, 1931 1,920,572 Lacke Aug. l, 1933 2,269,800 Wetzel Jan.' 13, 1942 Y 2,603,421 Nioshal't -iuly 15,1952

OTHER REFERENCES Westinghouse Centrafire, Bulletin, published .1950 by the Westinghousev Electric Corporation, 16 pp. (only y p the back cover relied upon). 

